Production of 2-methyl-2-butene



Feb. 22,-1966 ROBERTA. SANFORD OONAL D K. WU/VflfRZ/(H ROE-RT L. FOSTER 9 I INVENTORS amzwwhzm ATTORNEYS United States Patent 3,236,908 PRODUCTION OF Z-METHYL-Z-BUTENE Robert A. Sanford, Homewood, Donald K. Wunderlieh,

Chicago, and Robert L. Foster, Homewood, 111., as-

signors to Sinclair Research, Inc., New York, N.Y., a

corporation of Delaware Filed July 23, 1962, Ser. No. 211,610 8 Claims. (Cl. 260-6832) Our invention relates to the production of 2-methyl- Z-butene from the effluent from the catalytic cracking of gas oil. More particularly our invention relates to a method employing selective isomerization of 2-methyll-butene for the production of 2-methyl-2-butene.

Typical of C containing hydrocarbon streams obtained in present commercial processes is fluid catalytically cracked gasoline. The C portion of such gasoline contains two of the isoamylene isomers, namely, 2-methyl-l-butene and 2-methyl-2-butene in a weight ratio from about 1:1 to about 1:4 and most often about 1:2, respectively. One of the methods suggested for the recovery of such isomers from hydrocarbon streams comprises the fractionation of the C component. In order to illustrate the problems involved in such a fractionation process, the following table shows a typical analysis of the C portion of a catalytically cracked gasoline.

T 0 recover the isoamylene content of such a mixture by conventional fractionation requires four steps:

(1) Taking l-pentene and lighter components overhead, i.e. effecting a split between l-pentene and Z-methyll-butene;

(2) Taking the Z-methyl-l-butene component overhead, i.e. effecting a split between Z-methyl-l-butene and n-pentane;

(3) Taking n-pentane, trans-Z-pentcne and cis-2- pentene overhead, i.e., splitting between cis-2-pentene and Z-methyI-Z-butene; and

(4) Taking the 2-methyl-2-butene overhead, i.e., effecting a split between 2-methyl-2-butene and heavier C materials normally carried over with the C fraction.

Thus, each of these four fractionations requires the separation of components boiling within a narrow range and two of the fractionations require the separation of components boiling within a range of 25 F. Such fractionations require the employment of towers having a large number of plates and high reflux ratios. These towers require large capital and operating expenses.

It is the purpose of this invention to provide a method for producing isoamylene (predominately 2-methyl-2- butene) from the Z-methyl-l-butene present in catalytic gasoline, in which a liquid-phase, ambient-temperature, selective isomerization step is used considerably to reduce the fractionation equipment requirements.

Our invention provides a process for the production of 2-methyl-2butene from the eflluent from the catalytic cracking of gas oil. A minor portion of the cracked efiiuent can also be derived by thermal cracking. It should be pointed out that the cracking in these instances is nonhydrogenative, i.e., free hydrogen is not added to the 3,236,908 Patented Feb. 22, 1966 system. Our process includes fractionating such effluent to produce an overhead fraction consisting essentially of 2-methyl-1-butene and lower boiling C hydrocarbons substantially free of higher boiling materials. The fraction thus obtained is then admixed with sulfuric acid of from 60 to 70% by weight concentration with respect to water in order to isomerize 2-methyl-1-butene to 2-methyl-2-butene. The sulfuric acid phase is separated from the hydrocarbon phase and the hydrocarbon phase is then fractionated to recover 2-methyl-2-butene as product. After separation from the hydrocarbon phase, the acid phase can again be employed in the isomerization of Z-methyl-l-butene to 2-methyl-2-butene without purification. Thus, in a continuous process the separated acid phase can be directly recycled and in a batch process the separated acid phase can be directly admixed with a new batch of the hydrocarbon fraction.

In the process of our invention the first fractionation effects a separation essentially between 2-methyl-1-butene and lower boiling C s on the one hand and n-pentane and higher boiling hydrocarbons on the other hand. Referring to Table I it will be seen that such fractionation is effected between components having boiling points 8.9 F. apart and therefore the fractionation is relatively easy. The lower boiling fraction is then contacted with sulfuric acid which catalyzes the isomerization of the 2-methyll-butene (boiling point 88 F.) to 2-methyl-2-butene (boiling point 101.3 F.). As a result of the initial fractionation and isomerization, the final fractionation to recover the 2-methyl-2-butene is primarily a separation between materials of approximately 13 F. difference in boiling point rather than the 2 or 2.5 F. difference in a Separation of Z-methyl-l-butene or 2-methyl-2-butene from adjacent lighter materials in the original C feedstock.

In carrying out the acid contact step of our process, ambient temperatures and pressures can be employed. Preferably, the temperature is in the range from 50 to F. and the pressure is essentially atmospheric. While, as mentioned above, the ratio of 2-methyl1- butene to Z-methyl-Z-butene in the initial C fraction is about 1:1 to 1:4, after isomerization at a temperature of about 50-100 F., the ratio is about 1:9. The weight hourly space velocity of pounds of fresh hydrocarbon feed charged per hour per pound of 60 to 70% aqueous sulfuric acid inf the reactor can be in the range from about 2 to about 30' and preferably is from about 8 to about 15. The hydrocarbon-acid mixture from the contact zone can be separated into an acid phase and a hydrocarbon phase by settling. Preferably, the hydrocarbon phase is retained in the settling zone for a period of from about 20 to about 60 minutes and the acid phase is retained for about 5 to about 30 minutes. After separation, the acid phase, which can contain from about 28 to about 50 weight percent tertiary C olefins, advantageously is directly returned to the acid contact step. The invention hence provides a process whereby the removal of absorbed tertiary olefins from the acid phase is obviated.

In order to illustrate the process of our invention, reference is made to the following example which is to be considered with the attached drawing which shows in schematic form the process equipment employed.

EXAMPLE A stream of light fluid catalytic gasoline is fed to a first fractionator 10 by means of line 12. The stream of line 12 is flowing at the rate of 332 barrels per hour of C and higher boiling hydrocarbons, 20 barrels per hour of 2 methyl-l-butene and 148 barrels per hour of other C bydrocarbons. The tower 10 is a conventional fractionator 10 feet in diameter containing 150 bubble cap trays.

Tower is operated to make a close split between the n-pentane and the Z-methyl-l-butene components of the stream of line 12. About 95 percent of the 2-methyl-1- butene in the feed and essentially all of the lower boiling components are taken overhead from tower 10 by means of line 14 while essentially all of the n-pentane and heavier materials are removed from the tower as bottoms by means of line 16. The stream of line 16 can be sent to the refinery gasoline pool.

The tower overhead of line 14, which is flowing at the rate of approximately 84 barrels per hour, is passed by means of pump 18 and line 20 through heat exchanger 22, Where it is cooled by refrigeration, and is then introduced into contactor 26 by means of line 24. Contactor 26 operates at a temperature of 70 F. and a pressure of one atmosphere. Aqueous sulfuric acid having a sulfuric acid concentration of 65 percent by weight is introduced into contactor 26 by means of line 36. The weight hourly space velocity of pounds of hydrocarbon introduced by line 24 per hour per pound of aqueous sulfuric acid in contactor 26 is 10.

The hydrocarbon-sulfuric acid mixture is removed from contactor 26 by means of line 28 and passed to settling tank 30 which is sized to give a settling time of 30 minutes for the hydrocarbon phase and 10 minutes for the acid phase. The separated acid phase is removed from settling tank 30 by means of line 32 and is passed by means of pump 34 and line 36 back to contactor 26. The acid phase removed from settling tank 30 contains about 23 weight percent of isoamylene and in order to maintain the activity of the sulfuric acid catalyst and further to prevent emulsion problems, a small portion of the recycle acid (about 0.5%) is continuously withdrawn by means of line 38 and fresh make-up acid is added by means of line 40, both of which lines connect to line 36.

The hydrocarbon phase is removed from settling tank 30 by means of line 42 and this stream flows at the rate of about 18 barrels per hour of 2-methyl-2-butene, 2 barrels per hour of 2-methyl-1-butene and 64 barrels per hour of other C hydrocarbons. The hydrocarbon phase of line 42 is caustic and water washed to remove traces of entrained acid. Thus, a stream of aqueous sodium hydroxide is introduced into line 42 by means of line 44 and the combined stream is then passed through mixer 46 and into settling tank 48. Aqueous caustic is removed from settling tank 48 by means of line 50 and is recycled by means of pump 52 and line 44. Fresh aqueous sodium hydroxide is added to line 50 by means of line 54 and spent caustic is removed from tank 48 by means of line 56. The caustic washed hydrocarbon is removed from tank 48 by means of line 58. Water is added to the caustic washed stream of line 58 by means of line 60 and the combined stream is passed through mixer 62 and into tank 64. Water is removed from tank 64 by means of line 66 and the caustic and water washed hydrocarbon stream is removed from tank 64 and passed by means of line 68 to fractionator 70 for a final distillation. Fractionator 70 is 6 to 7 feet in diameter and contains about 100 bubble cap trays.

Table II shows the splits of the major components obtained in the final distillation effected in fractionator 70.

An overhead stream flowing at the rate of approximately 64 barrels per hour is removed from fractionator 70 by means of line 72 and sent to the gasoline pool. The stream from the bottom of tower 70 is removed by means of line 74 and passed to product storage tank (not shown). An isoamylene product having a purity of almost 95 percent is recovered from tower 70.

In some situations, where product specifications require the removal of the small amount of isoamylene dimer which is always present in the product from the isomerization step, it will be necessary to take the isoamylene product overhead in a small final tower (not shown in FIGURE I).

Thus, it can be seen that the process of our invention provides for the production of 2-methyl-2-butene without the necessity of employing a series of closely controlled fractionation steps.

We claim:

1. A method for producing 2-methyl-2-butene from an efiluent obtained from the catalytic cracking of gas oil which comprises fractionating said effiuent to effect a separation between an overhead hydrocarbon fraction consisting essentially of 2-methyl-1-butene and lower boiling C hydrocarbons and a fraction consisting essentially of n-pentane and higher boiling hydrocarbons, including 2-methyl-2-butene, admixing said overhead fraction with sulfuric acid of from 60 to 70% by weight concentration to isomerize Z-methyl-l-butene, separating the sulfuric acid phase from the hydrocarbon phase and fractionating the hydrocarbon phase to recover 2-methyl-2- butene therefrom.

2. The method of claim 1 in which the hydrocarbon fraction is admixed with the sulfuric acid at the rate of from about 2 to about 30 pounds of said hydrocarbon fraction per hour per pound of 60 to 70 weight percent sulfuric acid.

3. The method of claim 1 in which the hydrocarbon fraction is admixed with the sulfuric acid at a temperature in the range from about to about 100 F.

4. The method of claim 1 which further includes admixing the separated sulfuric acid phase with fresh hydrocarbon fraction consisting essentially of Z-methyl-lbutene and lower boiling C hydrocarbons.

5. A method for producing 2-methyl-2-butene from an efiiuent obtained from the fluid catalytic cracking of gas oil which comprises fractionating at atmospheric pressure, said efliuent to effect a separation between an overhead fraction consisting essentially of 2-methyl-l-butene and lower boiling C hydrocarbons and a fraction consisting essentially of n-pentane and higher boiling hydrocarbons, including 2-methyl-2-butene, admixing said overhead fraction with sulfuric acid of about to by weight concentration at a rate of about 8 to 15 pounds of said overhead fraction per hour per pound of sulfuric acid to isomerize 2-met'hyl-1-butene to 2-methyl-2-butene, separating the sulfuric acid phase from the hydrocarbon phase by settling, and fractionating the hydrocarbon phase at atmospheric pressure to recover 2-methyl-2-butene.

6. The method of claim 5 which further includes admixing the separated sulfuric acid phase with fresh hydrocarbon fraction consisting essentially of Z-methyl-lbutene and lower boiling C hydrocarbons.

7. The method of claim 4 wherein the separated sulfuric acid phase contains from about 2850 weight percent tertiary C olefin.

8. The method of claim 6 wherein the separated sulfuric acid phase contains from about 2850 weight percent tertiary C olefin.

References Cited by the Examiner UNITED STATES PATENTS 2,434,634 1/1948 Bates 260-683.2, 2,463,873 3/1949 Heinrich 260--683.2 X 2,591,367 4/1952 McAllister 260-6832 ALPHONSO D. SULLIVAN, Primary Examiner. 

1. A METHOD FOR PRODUCING 2-METHYL-2-BUTENE FROM AN EFFLUENT OBTAINED FROM THE CATALYTIC CRACKING OF GAS OIL WHICH COMPRISES FRACTIONATING SAID EFFLUENT TO EFFECT A SEPARATION BETWEEN AN OVERHEAD HYDROCARN FRACTION CONSISTING ESSENTIALLY OF 2-METHYL-1-BUTENE AND LOWER BOILING C5 HYDROCARBONS AND A FRACTION CONSISTING ESSENTIALLY OF N-PENTANE AND HIGHER BOILING HYDROCARBONS, INCLUDING 2-METHYL-2-BUTENE, ADMXING SAID OVERHEAD FRACTION WITH SULFURIC ACOF OF FROM 60 TO 70% BY WEIGHT CONCENTRATION TO ISOMERIZE 2-METHYL-1-BUTENE, SEPARATING THE SULFURIC ACID PHASE FROM THE HYDROCARBON PHASE AND FRACTIONATING THE HYDROCARBON PHASE TO RECOVER 2-METHYL-2BUTENE THEREFROM. 